During the supply of anesthesia, the gaseous anesthetic agent inhaled by the patient is generally formed of oxygen, nitrogen, nitrous oxide and an inhalation anesthetic agent. Inhalation anesthetics are typically in liquid form at administration temperatures, and an anesthetic vaporizer is implemented to convert the liquid into gas. Anesthetic vaporizers have a drug reservoir for storing the supply of the agent to be vaporized. The vaporized anesthetic is administered for the patient to inhale by means of a carrier gas flow.
Vaporizer reservoirs are provided with fill conduits and valves by way of which inhalation liquids may be added to the container or, when necessary, drained therefrom. Liquid is added to the vaporizer reservoir by either a filling device that is specifically designed for the anesthetic agent or by directly pouring the anesthetic agent into a filling hopper. It is a characteristic of the filling device that it can only be fixed to the storage container for a desired, single type of an anesthetic liquid to be transferred to the vaporizer.
The filling device incorporates a liquid flow conduit and a gas flow conduit. The filling of the drug reservoir for the anesthetic vaporizer is based on the exchange of volume in the vaporizer and the storage container for the anesthetic liquid. When the anesthetic liquid flows into the vaporizer, an equivalent volume of gas flows out of the vaporizer and back into the storage container. Correspondingly, when anesthetic liquid flows out of the storage container, an equivalent volume of gas flows back into the storage container. The filling of the vaporizer typically stops if the replacement gas flow is exhausted or blocked.
It is essential for the operation of the vaporizer that the vaporizer drug reservoir is not filled over a maximum limit. If the vaporizer reservoir is overfilled, the result may be that an overly high dose of anesthetic agent is delivered. Otherwise, depending upon the vaporizer, an overfilled reservoir may trigger a shutdown and could thereby cause the patient to prematurely awaken. One problem with conventional anesthetic vaporizers is that, under certain circumstances, their drug reservoirs can be overfilled. Some exemplary circumstances under which the drug reservoirs can overfill include situations wherein the anesthetic vaporizers are tilted or when they are being filled with an anesthetic agent having a high vapor pressure.